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The thermoreversible sol-gel transition for an ionic liquid (IL) solution of isotactic-rich poly (N-isopropylacrylamides) (PNIPAMs) is investigated by rheological technique. The meso-diad content of PNIPAMs ranges between 47% and 79%, and molecular weight (Mn) is ~35,000 and ~70,000 g/mol for two series of samples. PNIPAMs are soluble in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide ([BMIM][TFSI]) at high temperatures but undergo a gelation with decreasing temperatures. The transition temperature determined from G&rsquo, G&rdquo, crossover increases with isotacticity, consistent with the previous cloud-point result at the same scanning rate, indicating imide groups along the same side of backbones are prone to be aggregated for formation of a gel. The transition point based on Winter-Chambon criterion is on average higher than that of the G&rsquo, crossover method and is insensitive to tacticity and molecular weight, since it correlates with percolation of globules rather than the further formation of elastic network (G&rsquo, &gt, ). For the first time, the phase diagram composed of both G&rsquo, crossover points for gelation and cloud points is established in PNIPAM/IL mixtures. For low-Mn PNIPAMs, the crossover-point line intersects the cloud-point line. Hence, from solution to opaque gel, the sample will experience two different transitional phases, either clear gel or opaque sol. A clear gel is formed due to partial phase separation of isotactic segments that could act as junctions of network. However, when the partial phase separation is not faster than the formation of globules, an opaque sol will be formed. For high-Mn PNIPAMs, crossover points are below cloud points at all concentrations, so their gelation only follows the opaque sol route. Such phase diagram is attributed to the poorer solubility of high-Mn polymers for entropic reasons. The phase diagram composed of Winter-Chambon melting points, crossover points for melting, and clear points is similar with the gelation phase diagram, confirming the mechanism above.

Nanohybrids of graphene with water soluble polymer were synthesized using ‘grafting from’ method. GO, prepared by modified Hummers’ method, was first reacted with sodium azide. Alkyne-terminated RAFT-CTA was synthesized by reaction of propargyl alcohol and S-1-dodecyl-S’-(α,α‘-dimethyl-α”-acetic acid) trithiocarbonate. RAFT-CTA was grafted onto the GO sheets by facile click-reaction and subsequently, N-isopropylacrylamide (NIPAM) and N-ethyleacrylamide (NEAM) were polymerized on graphene sheets via RAFT polymerization method. The respective copolymers with different ratios were also prepared. The nanohybrids were characterized by FTIR, XRD, TGA, Raman, SEM, and AFM. Both SEM and AFM clearly showed rod-like structures for rGO-PNEAM. XRD showed a small peak at 2θ = 19.21°, corresponding to d-spacing ≈ 4.6 Å. In addition, the nanohybrids showed a very broad temperature range for the LCST in water between ca. 30 and 70 °C.

WOS: 000347696100012, Macroporous poly(N-ethylacrylamide) (PNEAM) hydrogels have been prepared in a methanol-water (1:1, v/v) mixture in the presence of 0, 0.05, 0.1, 0.15, and 0.2 M yttrium trifluoromethanesulfonate [Y(OTf)(3)] Lewis acid (LA) concentrations. SEM micrographs show that the resulted hydrogels are highly porous. Swelling ratios of all the hydrogels in water decrease with the increase in the temperature, and the hydrogels show lower critical solution temperature (LCST) volume phase transition at around 75 A degrees C. LCST of PNEAM homopolymers gradually increases with the increase in the isotacticity of the polymers. Moreover, the hydrogels show cononsolvency in different methanol-water mixtures at 50 A degrees C. Deswelling rate of the hydrogels prepared in the presence of LA is higher than the gel prepared in the absence of LA and this rate increases with increase in the LA concentration. The reswelling rate of the hydrogels also follows the same order, that is reswelling rate also increases with the increase in the LA loading in the gels. All these results are explained on the basis of the formation of the highly porous hydrogels with a higher isotactic PNEAM chain segment in a methanol-water mixture in the presence of LA., TUBITAK, Government of TurkeyTurkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK); TUBITAKTurkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [211T016]; Bulent Ecevit University Research FundBulent Ecevit University [BEU-2012-10-03-13], We gratefully acknowledge the financial support from TUBITAK, Government of Turkey, through 2216 fellowship program for the foreign citizens (CSB). This work was also supported by both TUBITAK (grant no. 211T016) and the Bulent Ecevit University Research Fund (#BEU-2012-10-03-13). We personally thank Elvan Sulu for her technical assistance.